1. Field of the Invention
This invention relates to nickel-chromium-silicon alloys. More particularly it relates to thin ductile Ni-Cr-Si metal foils having a density of about 100 percent.
2. Prior Art
The nickel-chromium-silicon alloys in the nickel-rich corner of the Ni-Cr-Si ternary triangle such as the composition specified in Aeronautical Material Specification 4782, (Ni.sub.62.3 Cr.sub.18.9 Si.sub.18.8) have been used in the form of powders, pastes and less than 100 percent dense foil fabricated from powder, because of the brittle nature of these alloys when these alloys have a silicon content greater than 6 atomic percent.
The disadvantages of using powder and pastes is that the alloy when molten, has to flow into the joint and fill up the gap between the mating parts. The flow of the molten alloy is strongly sensitive to the brazing environment and under non-ideal conditions the alloy may not flow through the joint gap. Also the organic binders in the pastes leave a residual contamination which alter the properties of the brazed joint. The use of sintered foil which has a density of less than 100 percent will result in voids in the brazed joint.
U.S. Pat. No. 3,856,513 discloses a wire product where alloys are represented by the formula T.sub.i X.sub.j wherein T is a transition metal and X is Al, Sb, Be, B, Ge, C, In, P, Si or Sn. The transition metals include metals from Groups IB, IIIB, IVB, VB, VIB, VIIB and VIIIB of the periodic table. The patent also teaches that the alloys contain at least 50 percent amorphous phase. As is apparent from that description, about 280 binary alloys are disclosed and an infinite number of alloys when mixtures of metals are used for T and X. The only alloys specifically disclosed are Pd.sub.77.5 Cu.sub.6 Si.sub.16.5 and Ni.sub.40 Pd.sub.40 P.sub.20. The patent also discloses ternary alloys of the formula M.sub.a Y.sub.b Z.sub.c in sheet, ribbon and powder form wherein M is Ni, Fe, Cr, Co or V, Y is P, C or B and Z is Al, Si, Sn, Sb, Ge, In or Be.
It is believed that a 100 percent dense foil of the Ni-Cr-Si alloys which are ductile in nature and is therefore suited for fabricating into brazing preforms of a required geometry, by conventional stamping or photo etching techniques, without cracking would be an advancement in the art.
The advantages of the present invention over the present techniques is the ability to make ductile foil which would be normally brittle if made by conventional techniques. The process of making ductile foil also results in foil of uniform composition which is highly desirable for obtaining brazed joints with a high degree of reproductibility. Such a ductile foil is especially suitable for fabricating into brazing preforms of required geometry.